How much is the Prmiere can output the biggest support gear vr 3D 360 video

Hi there

I'm doing a sequence frame animation,The size of the picture is 8 k * 2 k, but when I want to output the H264 video size is only 4 k * 1 k, and the output video quality is very poor,Is there any way to improve the output quality, or other coder that is supported by  gear vr